附加屏蔽气体的大气等离子喷涂对热障涂层性能影响

对比研究了附加屏蔽气体的大气等离子喷涂和普通大气等离子喷涂对热障涂层组织结构和性能的影响．结果表明,附加屏蔽气体的大气等离子喷涂粘结层表面未熔或半熔粒子较少,涂层中氧化物夹杂和孔隙率降低,热障涂层在1080℃下具有更好的抗氧化性能．附加屏蔽气体的大气等离子喷涂的热障涂层具有更好的抗氧化性能的原因,在于外加保护气氛减轻了...     

大气等离子喷涂锆酸镧热障涂层

利用自制的稀土元素复合掺杂锆酸镧热喷涂粉末,采用大气等离子喷涂技术,在镍基高温合金表面制备La1.6Nd0.4Ce1.0Zr1.0O7(LNCZ)热障涂层,研究了喷涂参数对涂层沉积率、显微结构、结合强度及抗热震性能的影响。结果表明,增大喷涂功率,降低送粉速率可以有效地提高涂层的沉积率,但对涂层结合和抗热震性能不利。减小喷涂距离不仅提高沉积率,还有利于获得孔径细小、孔隙率适中的层状组织结构,该结构对提高涂层的抗热震性能极为有利。采用DH-1080大气等离子喷涂设备制备LNCZ涂层较好的喷涂条件为:功率40 kW,喷涂距离9 cm,送粉速率12 g/min。     

热喷涂NiCr/Cr3C2、NiCrCoAlY、涂层的微观组织结构及抗震性能

研究分析了等离子喷涂NiCr／Cr3C2、NiCrCoAlY涂层的微观组织结构，并对2种涂层进行了显微硬度及抗热震性能实验。结果表明：NiCr／Cr3C2涂层的硬度高于NiCrCoAlY涂层．而NiCrCoAlY涂层的抗热震性能优于NiCr／Cr3C2涂层。     

等离子喷涂热障涂层的热循环氧化行为研究

本文采用大气等离子喷涂在HA188合金基材上制备NiCrAlY+YSZ热障涂层，并进行了1100 oC、1120 oC和1150 oC三个温度点的高温循环氧化行为对比研究。结果表明，随着考核温度的升高，热障涂层热循环失效寿命显著下降，失效主要是由YSZ/NiCrAlY界面附近YSZ 层中裂纹形成和扩展导致。循环失效后的YSZ与制备态的相结构一样，均为非平衡四方相t"-ZrO2，未发生t"→c+m相变。在热循环过程中，YSZ/NiCrAlY界面形成的热生长氧化物层（Thermally Grown Oxide, TGO）增厚基本符合“抛物线”规律，并且YSZ中裂纹的产生和扩展与TGO的增厚直接相关。     

三种热障涂层的组织性能

采用等离子喷涂技术制备了三种不同材料的热障涂层(TBC),对涂层进行了组织性能的分析比较.结果表明,Al-1075的TBC结合强度最高,为 24.66 MPa,具有良好的抗热震性能;KF-230的TBC结合强度最低,为 16.06 MPa;LG-210的TBC结合强度居中,抗热震性能最差.分析认为,氧化物层(TGO)在热障涂层中的失效起至关重要的作用,TGO是裂纹的产生源,是裂纹扩展的通道,是热障涂层系统中的最薄弱环节.因此抑制TGO是提高涂层结合强度、改善涂层抗热震性能的重要措施.     

热障涂层的研究现状与发展趋势

热障涂层是一类高温防护涂层,由于其应用的广泛性,已成为近年来涂层研究领域的热点之一。对热障涂层国内外的研究进展进行了综述,重点阐述热障涂层成分的选择、热障涂层的结构设计、热障涂层的制备工艺、热障涂层的失效机理、寿命预测以及热障涂层的发展趋势。     

Superior thermal barrier coatings using solution precursor plasma spray

A novel process, solution precursor plasma spray (SPPS), is presented for depositing thermal barrier coatings (TBCs), in which aqueous chemical precursors are injected into a standard direct current plasma spray system. The resulting coatings microstructure has three unique features: (1) ultra fine splats (1 μm), (2) nanometer and micron-sized interconnected porosity, and (3) closely spaced, through-thickness cracks. Coatings over 3 mm thick can be readily deposited using the SPPS process. Coating durability is excellent, with SPPS coatings showing, in furnace cycling tests, 2.5 times the spallation life of air plasma coatings (APS) and 1.5 times the life of electron beam physical vapor deposited (EB-PVD) coatings. The conductivity of SPPS coatings is lower than EB-PVD coatings and higher than the best APS coatings. Manufacturing cost is expected to be similar to APS coatings and much lower than EB-PVD coatings. The SPPS deposition process includes droplet break-up and material arriving at the deposition surface in various physical states ranging from aqueous solution, gel phase, to fully-molten ceramic. The relation between the arrival state of the material and the microstructure is described.     

Thermal stability and mechanical properties of thick thermal barrier coatings with vertical type cracks

The thermal stability and failure mechanism of thick thermal barrier coatings (TBCs) with and without vertical type cracks were investigated through the cyclic thermal exposure and thermal-shock tests. The TBC systems with thickness of about 2000 µm in the top coat were prepared by an air plasma spray (APS) on the bond coat of about 150 µm in thickness prepared by APS. The adhesive strength values of the as-prepared TBCs with and without vertical type cracks were determined to be 24.7 and 11.0 MPa, respectively, indicating the better interface stability in the TBC with vertical type cracks. The TBC with vertical type cracks shows a better thermal durability than that without vertical type cracks in the thermal cyclic exposure and thermal-shock tests. The hardness values of the as-prepared TBCs with and without vertical type cracks were found to be 6.6 and 5.3 GPa, respectively, which were increased to 9.5 and 5.5 GPa, respectively, after the cyclic thermal exposure tests. These results indicate that the vertical type cracks developed in the top coat are important in improving the lifetime performance of thick TBC in high temperature environment.     

Temperature measurements and adhesion properties of plasma sprayed thermal barrier coatings

Metal-ceramic coatings have been widely used for industrial applications, mainly in the gas turbine and diesel engine industries as thermal barrier coatings (TBCs). Conventional thermal barrier coatings consist of a metallic bond coat and an insulating ceramic topcoat. Temperatures and temperature gradients in the coating during plasma spraying play an important role on the final coating quality, especially the temperature of the particles just hitting the substrate surface. In this work, metal-ceramic coatings were applied on nickel-superalloy substrates. The temperatures of both the coating surface and substrate were measured during spraying. The adhesion of the coatings was determined using ASTM C 633 and correlated with the measured temperatures. Optical pyrometry and thermocouples were used to measure the interfacial and substrate temperatures, respectively. Temperature was shown to have a significant influence where lower interfacial temperatures were found to result in lower adhesion values.     

Anisotropic thermal conductivities of plasma-sprayed thermal barrier coatings in relation to the microstructure

Anisotropic thermal conductivities of the plasma-sprayed ceramic coating are explicitly expressed in terms of the microstructural parameters. The dominant features of the porous space are identified as strongly oblate (cracklike) pores that tend to be either parallel or normal to the substrate. The scatter in pore orientations is shown to have a pronounced effect on the effective conductivities. The established quantitative microstructure-property relations, if combined with the knowledge of the processing parameters-resulting microstructure connections, can be utilized for controlling the conductivities in the desired way.     

冷喷涂和低压等离子喷涂Ni-Ti涂层：组织和性能

采用原子比1：1的Ni和Ti为原料,通过冷喷涂(CS)和低压等离子喷涂(LPPS)制备了Ni-Ti复合涂层,研究喷涂工艺对涂层的组织(孔隙率、相组成和显微组织)和性能(硬度、耐磨性和耐蚀性)的影响。结果表明：两种涂层均未发生明显的氧化,但表现出不同的组织结构。高速碰撞后的颗粒发生严重塑性变形使CS涂层具有低的孔隙率,且XRD未检测到其它的相生成;层片状结构的LPPS涂层内部形成了Ni-Ti金属间化合物相,其表现出高的显微硬度和低的磨损率。此外,LPPS涂层高的腐蚀电位和低的腐蚀电流密度,表明其高的耐蚀性。     

Non-destructive evaluation of plasma sprayed functionally graded thermal barrier coatings

Acoustic emission (AE) as a non-destructive evaluation technique has recently been used in a number of studies to investigate the performance and failure behavior of plasma sprayed thermal barrier coatings. The mechanism of coating failure is complex, especially when considering the composite nature of the coating. In the present paper, the thermal shock tests with in situ acoustic emission are used to study the cracking behavior of plasma sprayed functionally graded thermal barrier coatings. Each thermal cycle consists of 8 min heating in the furnace at 1000°C and 8 min cooling from 1000°C to the room temperature by a compressed air jet. The AE signals are recorded during the quench stage. Three, four and five layer functionally graded coatings have been tested. The results show that the five layer functionally graded coatings appear to have the best thermal shock resistance in the specimens tested, because of the gradual changes in material properties. Higher AE energy counts and cumulative counts recorded by the tests are associated with the macro-crack initiation and growth. On the other hand, micro cracking and phase transformation only give rise to lower AE signals.     

微弧等离子喷涂制备莫来石/金属复合热障涂层

运用微弧等离子喷涂制备了莫来石/金属复合热障涂层.研究了涂层的微观结构、结合强度、隔热性能和抗热震性能.复合涂层结构为莫来石颗粒被"包裹"在金属层片状结构中;涂层的结合强度大于30 MPa.随着涂层中莫来石含量的增加,涂层的隔热性能有所提高,随涂层表面温度的升高,涂层的隔热温度也不断提高,涂层的最高隔热温度为125℃.1 150℃的水淬热震试验表明,基体变形是导致涂层失效的重要原因之一,随着涂层中莫来石含量的增加,涂层的抗热震次数先增加后减小,粉末中莫来石含量为40%的涂层的抗热震性能最好,抗热震次数最多为72次.     

超音速等离子喷涂层的组织及性能分析

用超音速等离子喷涂技术制备了NiCrBSi涂层,并对涂层的组织性能进行了综合分析.用扫描电镜和能谱仪分析了涂层的内部组织,用纳米压痕法测试了硬度和弹性模量,用拉伸试验法测试了涂层与基体的结合强度,用X射线应力仪测定了涂层沿厚度方向的残余应力的分布.结果表明,涂层内部比较均匀,具有较低的孔隙率和氧化物含量,涂层的纳米显微...     

镀铝对7YSZ热障涂层冲刷性能的影响

采用磁控溅射在大气等离子喷涂的ZrO2?7%Y2O3(7YSZ)热障涂层表面制备一层厚度约15μm铝膜,对镀有铝膜的热障涂层样品在700、900°C分别保温1 h和5 h进行真空热处理。采用场发射?扫描电子显微镜对经真空热处理前后镀铝热障涂层的微观结构进行表征。采用X射线衍射和透射电子显微镜对经真空热处理前后镀铝热障涂层的物相变化进行分析。对等离子喷涂的7YSZ原始热障涂层和镀铝真空热处理后的热障涂层进行室温粒子冲刷性能对比。结果表明：镀铝热障涂层经真空热处理后在涂层表面出现疏松表层和致密底层,其成分主要为α-Al2O3,其中致密底层来源于Al膜与ZrO2的高温原位反应且该层有较高的显微硬度。此外,冲刷实验后发现镀铝真空热处理后热障涂层的冲刷性能比无镀铝热障涂层有较大的提高。     

等离子喷涂ZrO2-NiCoCrAlY梯度涂层的界面强化热处理工艺

在大气条件下经高温长时间保温后,ＺｒＯ２ＮｉＣｏＣｒＡｌＹ 梯度涂层中的ＮｉＣｏＣｒＡｌＹ 组元发生严重氧化, 形成大量的ＮｉＯ, Ａｌ２Ｏ３ 和Ｃｒ２Ｏ３ 等氧化物, 导致ＺｒＯ２ 表面层中产生粗大网状裂纹, 并最终导致ＺｒＯ２ 表面层碎裂而失效。对梯度涂层进行（９００ ℃） 保温（８ ｈ） 的真空热处理后, 涂层完好无损, ＮｉＣｏＣｒＡｌＹ 底层与ＴＣ４ 基体发生了冶金化学反应, 在涂层与基体界面形成了含ＮｉＴｉ, ＮｉＴｉ２ 和ＴｉＡｌ３ 等化合物的反应层, 涂层的抗热震性能得以显著地提高     

Comparison of thermal shock behaviors between plasma-sprayed nanostructured and conventional zirconia thermal barrier coatings

NiCoCrAlTaY bond coat was deposited on pure nickel substrate by low pressure plasma spraying(LPPS), and ZrO2-8%Y2O3 (mass fraction) nanostructured and ZrO2-7%Y2O3 (mass fraction) conventional thermal barrier coatings(TBCs) were deposited by air plasma spraying(APS). The thermal shock behaviors of the nanostructured and conventional TBCs were investigated by quenching the coating samples in cold water from 1 150, 1 200 and 1 250 ℃, respectively. Scanning electron microscopy(SEM) was used to examine the microstructures of the samples after thermal shock testing. Energy dispersive analysis of X-ray(EDAX) was used to analyze the interface diffusion behavior of the bond coat elements. X-ray diffractometry(XRD) was used to analyze the constituent phases of the samples. Experimental results indicate that the nanostructured TBC is superior to the conventional TBC in thermal shock performance. Both the nanostructured and conventional TBCs fail along the bond coat/substrate interface. The constituent phase of the as-sprayed conventional TBC is diffusionless-transformed tetragonal(t′). However, the constituent phase of the as-sprayed nanostructured TBC is cubic(c). There is a difference in the crystal size at the spalled surfaces of the nanostructured and conventional TBCs. The constituent phases of the spalled surfaces are mainly composed of Ni2.88Cr1.12 and oxides of bond coat elements.     

Thermal shock testing of thermal barrier coating/bondcoat systems

Various methods of thermal shock testing are used by aircraft and industrial gas turbine engine (IGT) manufacturers to characterize new thermal barrier coating systems in the development stage as well as for quality control. The cyclic furnace oxidation test (FCT), widely used in aircraft applications, stresses the ceramic/bondcoat interface, predominantly through thermally grown oxide (TGO) growth stress. The jet engine thermal shock (JETS) test, derived from a burner rig test, creates a large thermal gradient across the thermal barrier coating (TBC), as well as thermomechanical stress at the interface. For IGT applications with long high-temperature exposure times, a combination of isothermal preoxidation and thermal shock testing in a fluidized bed reactor may better represent the actual engine conditions while both types of stress are present. A comparative evaluation of FCT, JETS, and a combined isothermal oxidation and fluidized bed thermal shock test has been conducted for selected ceramic/bondcoat systems. The results and the failure mechanisms as they relate to the TBC system are discussed. A recommendation on the test method of choice providing best discrimination between the thermal shock resistance of the ceramic layer, the ceramic/bondcoat interface, and even substrate related effects, is given. This paper was presented at the 2nd International Surface Engineering Congress sponsored by ASM International, on September 15–17, 2003, in Indianapolis, Indiana, and appeared on pp. 520–29.     

Transient thermography testing of unpainted thermal barrier coating (TBC) systems

Test piece surfaces are sometimes coated with a black, energy absorbing paint before transient thermography is applied. This practice is not acceptable to some thermal barrier coating (TBC) manufacturers and servicers of these systems since thermal barrier coatings are porous so the paint contaminates the coating and it is very difficult and costly to remove. Unfortunately, unpainted TBC surfaces have low emissivity, and after service their colour is usually uneven. The low emissivity gives low signal levels and also problems with reflections of the incident heat pulse, while the variation in emissivity over the surface gives strong variation in the contrast obtained even in the absence of defects. Additionally, the TBC is translucent to mid-wavelength IR radiation which negatively affects the location of disbonds based on the thermal responses. This paper investigates the effects of uneven discolouration of the surface and of IR translucency on the thermal responses. It has been shown that unpainted TBC systems can be inspected reliably by using higher power flash heating equipment assembled with an IR glass filter and a long wavelength IR camera. The paper also shows that the problem with uneven surface emissivity can be overcome by applying 2nd time derivative processing of the log–log surface cooling curves.     

Al2O3对等离子喷涂热障涂层高温氧化及热震性能的影响

采用等离子喷涂 (PS)在GH5 36高温合金基材上制备了典型的双层热障涂层 (TBCs)和两种分别加入了Al2 O3 陶瓷成分的复合热障涂层。典型的TBCs采用Ni2 2Cr10AlY连接层与 8%Y2 O3 稳定的 (8YPSZ)顶层的双层结构 ;多层涂层分别采用Al2 O3 与Ni2 2Cr10AlY复合的连接层和Al2 O3 与 8YPSZ复合的顶层。3种类型试样的10 0h ,10 0 0℃静态氧化及 10 5 0℃热震试验的结果分析表明 :8YPSZ Al2 O3 的复合氧障层具有最佳的氧化阻力 ;Ni2 2Cr10AlY 8YPSZ双层涂层的热震阻力最佳 ,氧化阻力最差 ;连接层采用Ni2 2Cr10AlY Al2 O3 复合涂层具有热震和静态氧化条件下综合优良的高温热循环性能